CN111435742A - Positive electrode active material, positive electrode plate and sodium ion battery - Google Patents

Abstract

The present application discloses a positive electrode active material, a positive electrode piece and a sodium ion battery. The molecular formula of the positive electrode active material is Na _2+x Cu _h Mn _k M _l O _7-y , and in the molecular formula, M is a transition metal site doping Miscellaneous elements, and M is one of Li, B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, Sn, Ba and W one or more, 0≤x≤0.5, 0.1<h≤2, 1≤k≤3, 0≤l≤0.5, 0≤y≤1; among them, 2≤h+k+l≤3.5, 0.57≤( 2+x)/(h+k+l)≤0.9. The positive electrode active material provided by the present application can take into account high initial capacity, rate performance and cycle performance at the same time.

Description

Positive electrode active material, positive electrode plate and sodium ion battery

technical field

The application belongs to the technical field of energy storage devices, and in particular relates to a positive electrode active material, a positive electrode plate and a sodium ion battery.

Background technique

At present, lithium-ion batteries occupy the core position of power batteries. At the same time, lithium-ion batteries are also facing great challenges, such as the increasing shortage of lithium resources, the rising price of upstream materials, the lag in the development of recycling technology, and the recycling rate of old batteries. low issues. Na-ion batteries can use the de-intercalation process of sodium ions between the positive and negative electrodes to achieve charge and discharge, and the reserves of sodium resources are far more abundant and widely distributed than lithium, and the cost is far lower than that of lithium. Therefore, sodium-ion batteries have great potential. A new generation of electrochemical systems to replace lithium-ion batteries. However, currently widely studied cathode active materials for Na-ion batteries suffer from low capacity, poor rate capability and cycle performance, hindering the commercialization of Na-ion batteries.

SUMMARY OF THE INVENTION

In view of the problems existing in the background art, the present application provides a positive electrode active material, a positive electrode sheet and a sodium ion battery, aiming to enable the positive electrode active material to exhibit high capacity, and have both high rate performance and cycle performance.

In order to achieve the above purpose, a first aspect of the present application provides a positive electrode active material, the molecular formula of the positive electrode active material is Na _2+x Cu _h Mn _k M _l O _7-y , in the molecular formula, M is a transition metal site doping element, and M is one or more of Li, B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, Sn, Ba and W species, 0≤x≤0.5, 0.1<h≤2, 1≤k≤3, 0≤l≤0.5, 0≤y≤1; among them, 2≤h+k+l≤3.5, 0.57≤(2+x )/(h+k+l)≤0.9.

A second aspect of the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material according to the first aspect of the present application.

A third aspect of the present application provides a sodium-ion battery, the sodium-ion battery includes the positive electrode plate according to the second aspect of the present application.

Compared with the prior art, the present application at least has the following beneficial effects:

The positive electrode active material provided by the present application satisfies the molecular formula Na _2+x Cu _h Mn _k M _l O _7-y , and has a specific chemical composition, so that the positive electrode active material has high ionic conductivity and electrical conductivity, and high Therefore, the positive electrode active material has both high rate capability and cycle performance.

Further, when the cathode active material also has two higher charge-discharge voltage plateaus, the regions of the two charge-discharge voltage plateaus are long and flat, and the ratio of the voltage plateau capacity to the corresponding cycle full capacity is higher, which improves the The charge-discharge capacity development and material utilization rate of the positive electrode active material.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings that need to be used in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the drawings without any creative effort.

FIG. 1 is a first-round charge-discharge curve diagram of a sodium-ion battery provided in Example 6 of the present application.

FIG. 2 is a first-cycle charge-discharge curve diagram of the sodium-ion battery provided in Example 11 of the present application.

Detailed ways

In order to make the invention purpose, technical solutions and beneficial technical effects of the present application clearer, the present application will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application, but not for limiting the present application.

For the sake of brevity, only some numerical ranges are expressly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with any other lower limit to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, every point or single value between the endpoints of a range is included within the range, even if not expressly recited. Thus, each point or single value may serve as its own lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

In the description herein, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the numbers, and the meaning of “multiple” in “one or more” means two or more.

The above summary of this application is not intended to describe each disclosed embodiment or every implementation in this application. The following description illustrates exemplary embodiments in more detail. In various places throughout this application, guidance is provided through a series of examples, which examples can be used in various combinations. In various instances, the enumeration is merely a representative group and should not be construed as exhaustive.

Positive active material

First, the positive electrode active material according to the first aspect of the present application is explained. The molecular formula of the positive electrode active material is Na _{2+ x} Cu _h Mn _k M _l O _7-y , in which M is a transition metal site doping element, and M is Li, B, Mg, Al, K, Ca, Ti, One or more of V, Cr, Fe, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, Sn, Ba and W, 0≤x≤0.5, 0.1<h≤2, 1≤k ≤3, 0≤l≤0.5, 0≤y≤1.

The number of sodium atoms in the molecular formula is preferably 2 or more, which is conducive to improving the first cycle charge-discharge capacity of the positive electrode active material; the number of sodium atoms in the molecular formula is preferably less than 2.5, which is conducive to improving the stability of the positive electrode active material to air, water and carbon dioxide , reduce the capacity loss of the positive electrode active material during the charge-discharge cycle and storage process, and ensure that the positive electrode active material has a high capacity retention rate.

Further, in the molecular formula, 0.1<h≤2, 1≤k≤3, so that during the charging and discharging process, the electron transfer of Cu and Mn provides effective charge compensation for the de-intercalation and intercalation of sodium ions, thereby improving the positive electrode activity. The charge-discharge voltage platform of the material makes the cathode active material have a higher specific capacity.

Further, in the molecular formula, 2≤h+k+l≤3.5, and 0.57≤(2+x)/(h+k+l)≤0.9. With this chemical composition, the positive electrode active material can have fewer chemical composition defects, reduce the impurity phase in the material; improve the internal structure and structural stability of the positive electrode active material; and improve the migration of sodium ions and electrons in the positive electrode active material Therefore, the capacity of the positive electrode active material can be improved, and the polarization phenomenon can be reduced, so that the positive electrode active material has both high rate performance and cycle performance.

In some embodiments of the present application, the lower limit of (2+x)/(h+k+l) may be optionally selected from 0.57, 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, 0.72, 0.74, 0.75; The upper limit of (2+x)/(h+k+l) can be optionally selected from 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.80, 0.85, 0.90. The range of (2+x)/(h+k+l) may be composed of any numerical values of the lower limit value and the upper limit value.

Further, in the molecular formula, 0.6≤(2+x)/(h+k+l)≤0.8. The positive electrode active material has better comprehensive electrochemical performance.

Further preferably, 0.5≤h≤1.5, 1.5≤k≤2.5. With this chemical composition, the capacity retention rate of the positive electrode active material during the charge-discharge cycle process can be better improved.

Further preferably, 0.9≤h≤1.5, 1.5≤k≤2.5. As shown in FIG. 1, with this chemical composition, the positive electrode active material has a first discharge voltage plateau at 3.8V-4.1V and a second discharge voltage plateau at 3.4V-3.7V, and the charge-discharge voltage plateau is The region is wider and flatter, which increases the ratio of the voltage plateau capacity to the corresponding full-cycle capacity, and shows higher charge-discharge stability, which enables the cathode active material to have higher charge-discharge capacity and material utilization.

Further, the discharge capacity Q ₁ at the first discharge voltage platform, the discharge capacity Q ₂ at the second discharge voltage platform, and the full discharge capacity of the positive electrode active material satisfy: 30%≤(Q ₁ + Q ₂ )/Q×100%≦90%, preferably, 50%≦(Q ₁ +Q ₂ )/Q×100%≦80%.

Further, the discharge capacity Q1 of the positive electrode active material at the _first discharge voltage plateau is 30mAh/g～55mAh/g, and the discharge capacity _Q2 at the second discharge voltage plateau is 30mAh/g～75mAh/g, showing Higher voltage plateau discharge capacity.

The above-mentioned full discharge capacity of the positive electrode active material refers to the discharge capacity to discharge the sodium ion battery charged to the charge cut-off voltage to the discharge cut-off voltage.

The discharge voltage platform and discharge capacity of the positive electrode active material are obtained by combining the positive electrode active material with a weight ratio of 90:5:5, conductive carbon black and binder polyvinylidene fluoride The positive electrode and the negative electrode sodium metal sheet are composed of batteries, Charge at 0.1C constant current to the charge cut-off voltage, and then discharge at 0.1C to the discharge cut-off voltage.

Further preferably, 0.9≤h≤1.2, 1.5≤k≤2.5.

Preferably, in the molecular formula of the positive electrode active material of the present application, k/(h+l)≥1.4, which can further improve the capacity performance and kinetic performance of the positive electrode active material, so that the positive electrode active material has a higher first-round discharge specific capacity and rate performance. Further preferably, 1.6≤k/(h+l)≤6.

Optionally, in the molecular formula, 0<1≤0.5, by doping M element at the transition metal site, the specific capacity and rate performance of the positive electrode active material can be further improved.

The specific surface area of the positive electrode active material of the present application is preferably 0.01 m ² /g to 20 m ² /g. The specific surface area of the positive electrode active material is more than 0.01m ² /g, which ensures that the positive electrode active material has a small particle size, and the transport path of sodium ions and electrons in the positive electrode active material is short, which can improve the ion conductivity and the positive electrode active material. The electronic conductivity can improve the electrochemical kinetic performance and rate performance during the charge and discharge process, and can reduce the positive polarization phenomenon and improve the capacity retention rate during the charge and discharge cycle. In addition, the specific surface area of the positive electrode active material is below 20 m ² /g to ensure that the particle size of the positive electrode active material will not be too small, and the positive electrode active material with too small particle size will reduce the electrochemical performance of the positive electrode active material. The specific surface area of the positive electrode active material is less than 20 m ² /g, which can also effectively inhibit the agglomeration between particles of the positive electrode active material and ensure that the positive electrode has high rate performance and cycle performance.

When the specific surface area of the positive electrode active material is within the above range, the liquid absorption phenomenon during the preparation of the positive electrode slurry can also be reduced, and the solid content and particle dispersion uniformity in the positive electrode slurry can be improved, thereby improving the particle dispersion of the positive electrode active material layer. Uniformity and compaction density, thereby improving the specific capacity and energy density of the battery, and improving the rate performance and cycle performance of the battery.

Further preferably, the specific surface area of the positive electrode active material is 0.1 m ² /g to 15 m ² /g.

Preferably, the average particle diameter D _v 50 of the positive electrode active material is 0.5 μm to 25 μm, more preferably 1 μm to 15 μm.

Preferably, the tap density of the positive electrode active material is 0.5 g/cm ³ to 3.5 g/cm ³ , more preferably 1.5 g/cm ³ to 3.0 g/cm ³ .

Preferably, the compaction density of the positive electrode active material under a pressure of 8 tons is 2.5 g/cm ³ to 4.5 g/cm ³ , more preferably 3.5 g/cm ³ to 4.5 g/cm ³ .

Preferably, the powder resistivity of the positive electrode active material of the present application under a pressure of 12 MPa is 10Ω·cm˜300kΩ·cm, more preferably 20Ω·cm˜3kΩ·cm. The powder resistivity of the positive electrode active material is in the above range, which can better improve the rate performance and safety performance of the sodium ion battery.

The morphology of the positive electrode active material of the present application is preferably one or more of spheres, spheroids and polygonal flakes. The sphere and the sphere-like positive electrode active material are secondary particles composed of agglomeration of primary particles, and the morphology of the primary particles can be spherical, spherical or flake-like. The polygonal flake-shaped positive electrode active material may be one or more of a triangular flake shape, a square flake shape, and a hexagonal flake shape. The positive electrode active material with this morphology has a more stable structure during the charge-discharge cycle, thus enabling the sodium-ion battery to have better cycle performance.

Preferably, the positive electrode active material of the present application has a triclinic phase crystal structure or a hexagonal phase crystal structure. The positive electrode active material with this crystal structure has better structural stability, and the structural changes caused by the de-intercalation and intercalation of sodium ions are small, which constitutes a good host framework for reversible de-intercalation of sodium ions, so the positive electrode can be improved. Capacity development and cycle performance of active materials.

晶面产生的在15.8°～16.0°衍射角2θ处的第一衍射峰和由

晶面产生的在32.0°～32.2°衍射角2θ处的第二衍射峰，且第一衍射峰和第二衍射峰的强度比为5～30，第一衍射峰的半峰宽FWHM为0.02°～0.5°，第二衍射峰的半峰宽FWHM为0.02°～0.5°。Further, when the positive electrode active material of the present application has a triclinic phase crystal structure, it contains a

The first diffraction peak at the diffraction angle 2θ of 15.8°～16.0° produced by the crystal plane and the

The second diffraction peak generated by the crystal plane at the diffraction angle 2θ of 32.0°～32.2°, and the intensity ratio of the first diffraction peak and the second diffraction peak is 5～30, and the half width FWHM of the first diffraction peak is 0.02° ~0.5°, and the half width FWHM of the second diffraction peak is 0.02° to 0.5°.

When the positive electrode active material of the present application has a hexagonal phase crystal structure, it contains, under X-ray diffraction, a first diffraction peak at a diffraction angle 2θ of 15.8° to 16.0° due to the (002) crystal plane and a first diffraction peak due to the (004) crystal plane The second diffraction peak at the diffraction angle 2θ of 32.0°～32.2°, and the intensity ratio of the first diffraction peak and the second diffraction peak is 5～30, and the half width FWHM of the first diffraction peak is 0.02°～0.5° , the half width FWHM of the second diffraction peak is 0.02° to 0.5°.

The positive electrode active material having the above-mentioned crystal structure has good crystallinity, which is beneficial to further improve the capacity exertion and cycle performance of the positive electrode active material.

扫描2θ角范围为10°～90°，扫描速率为4°/min。The crystal structure of the positive electrode active material can be determined by using an X-ray powder diffractometer, for example, using a Brucker D8A_A25 X-ray diffractometer from BruckerAxS, Germany, with CuK _α ray as the radiation source, the ray wavelength

The scanning 2θ angle range was from 10° to 90°, and the scanning rate was 4°/min.

The specific surface area of the positive active material is the meaning known in the art, and can be measured with instruments and methods known in the art. For example, it can be tested by the nitrogen adsorption specific surface area analysis test method, and calculated by the BET (Brunauer EmmettTeller) method, wherein nitrogen The adsorption specific surface area analysis test can be carried out by the Tri Star II specific surface area and pore analyzer of Micromeritics Company of the United States.

The average particle diameter D _v 50 of the positive electrode active material has a meaning known in the art, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured with a laser particle size analyzer, such as a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

The morphology of the positive electrode active material can be measured with instruments and methods known in the art, for example, with a field emission scanning electron microscope, such as a SIGMA 500 high-resolution field emission scanning electron microscope from Carl Zeiss, Germany.

The tap density of the positive electrode active material can be measured with instruments and methods known in the art, for example, it can be conveniently measured with a tap density measuring instrument, such as a FZS4-4B type tap density measuring instrument.

The compacted density of the positive electrode active material can be measured by instruments and methods known in the art, for example, it can be conveniently measured by an electronic pressure testing machine, such as a UTM7305 electronic pressure testing machine.

Next, a method for preparing the positive electrode active material in the present application will be described. According to this production method, the above-described positive electrode active material can be produced. The preparation method includes the following steps:

S10, adding copper salt, manganese salt and optional salt containing M element to a solvent according to a stoichiometric ratio to prepare a mixed solution.

S20, adding a precipitant and a complexing agent to the mixed solution to prepare a reaction solution, and adjusting the pH value of the reaction solution within a predetermined range.

S30, the reaction solution is subjected to a co-precipitation reaction at a predetermined temperature and stirring speed, the obtained co-precipitated product is separated and collected, washed with an appropriate amount of solvent for several times, and dried at a predetermined temperature to obtain a transition metal source [Cu _h Fe _k Mn _l M _m ]X _u , wherein X is an anion taken from the precipitant, and h, k, l, m and u make the molecular formula [Cu _h Fe _k Mn _l M _m ]X _u electrically neutral.

S40 , mixing the transition metal source and the sodium source and performing sintering treatment, and after washing and drying the obtained sintered product, a positive electrode active material is obtained.

Among them, because different reactants in the solvent and the same reactant in different solvents will have different dissociation intensities, which will affect the reaction rate, including the rate of crystal nucleation and growth, thus affecting the chemical composition of the transition metal source , specific surface area, particle size, morphology and crystal structure, which ultimately affect the chemical composition, specific surface area, particle size, morphology and crystal structure of the cathode active material. In addition, the oxidation state of the metal atoms in the reactants also affects the electrochemical performance of the final product cathode active material.

In some preferred embodiments, in step S10, the copper salt is one or more of copper nitrate, copper chloride, copper sulfate, copper oxalate and copper acetate; the manganese salt is manganese nitrate, manganese chloride, manganese sulfate , one or more of manganese oxalate and manganese acetate; the salt containing M element is one or more of nitrate, chloride, sulfate, oxalate and acetate containing M element, such as When M is Fe, the salt containing M element is one of ferrous nitrate, ferric nitrate, ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, ferrous oxalate, ferric oxalate, ferrous acetate and ferric acetate One or more, for example, when M is Zn, the salt containing M element is one or more of zinc nitrate, zinc chloride, zinc sulfate, zinc oxalate and zinc acetate; the solvent is deionized water, methanol, ethanol, One or more of acetone, isopropanol and n-hexanol.

The concentration of reactants in the reaction solution is different. On the one hand, the dissociation rate of the reactants will be different, which will affect the reaction rate. Chemical composition and structure of materials.

In some preferred embodiments, in step S10, the total concentration of metal ions in the mixed solution is preferably 0.1 mol/L to 10 mol/L, more preferably 0.5 mol/L to 5 mol/L.

In the reaction system, the type and concentration of the precipitant will affect the reaction rate with the metal ions, and the type and concentration of the complexing agent have an important influence on the crystal nucleation and growth process of the transition metal source, and both will affect the transition metal source. Chemical composition and structure.

In some preferred embodiments, in step S20, the precipitating agent is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium bicarbonate and potassium carbonate; the complexing agent is ammonia water, One or more of ammonium carbonate, urea, hexamethylenetetramine, ethylenediaminetetraacetic acid, citric acid and ascorbic acid.

The pH value of the reaction system will affect the precipitation rate of each metal ion, thereby directly affecting the crystal nucleation and growth rate of the transition metal source, which in turn affects the chemical composition and structure of the transition metal source, and finally affects the chemical composition of the positive active material. structure. In order to realize the positive electrode active material of the present application, in step S20, the pH value of the reaction solution is controlled to be 6-13. When necessary, the pH value of the reaction solution can be adjusted by adjusting the type and content of the precipitant and/or complexing agent.

In some embodiments, step S20 includes:

S21, providing a precipitant solution and a complexing agent solution.

S22, adding the precipitant solution and the complexing agent solution to the mixed solution to obtain a reaction solution, and adjusting the pH value of the reaction solution within a predetermined range.

In some embodiments, step S21 includes dispersing a precipitant in a solvent to obtain a precipitant solution.

The solvent used for the precipitant solution can be one or more of deionized water, methanol, ethanol, acetone, isopropanol and n-hexanol.

Further, the concentration of the precipitant in the precipitant solution is preferably 0.5 mol/L to 15 mol/L, more preferably 2 mol/L to 10 mol/L.

In some embodiments, step S21 includes dispersing the complexing agent in a solvent to obtain a complexing agent solution.

The solvent used for the complexing agent solution can be one or more of deionized water, methanol, ethanol, acetone, isopropanol and n-hexanol.

Further, the concentration of the complexing agent in the complexing agent solution is preferably 0.1 mol/L to 15 mol/L, more preferably 0.5 mol/L to 10 mol/L.

In addition, the temperature of the reaction system will directly affect the rate and yield of the chemical reaction, and the reaction time will affect the growth process of the reaction product, which in turn affects the chemical composition and structure of the reaction product. Preferably, in step S30, the reaction temperature is 25°C to 70°C, and the reaction time is 10 hours to 60 hours.

The stirring rate in the reaction process will affect the mixing uniformity of the materials, and therefore has an important influence on the effect of complexation and precipitation reactions, which in turn affects the structure of the transition metal source. Preferably, in step S30, the stirring rate is 200 rpm to 1600 rpm. "rpm" means revolutions per minute, and represents the number of revolutions per minute of the stirring device.

The drying temperature in step S30 is preferably 80°C to 120°C, and the drying time is preferably 2 hours to 48 hours.

In step S40, the temperature and time of the sintering treatment will affect the specific surface area, particle size, morphology and crystal structure of the reaction product. Preferably, in step S40, the temperature of the sintering treatment is 500°C to 900°C, more preferably 550°C to 850°C; the time of the sintering treatment is preferably 4h to 30h, more preferably 8h to 20h.

In step S40, the sodium source may be one or more of sodium carbonate, sodium hydroxide and sodium nitrate.

In step S40, the sintering treatment may be performed in an air or oxygen atmosphere.

In steps S30 and S40, the detergent used for washing and the number of times of washing are not particularly limited, and can be selected according to actual needs, as long as the remaining ions on the surface of the product are removed. For example, the detergent can be deionized water.

In the preparation process of the positive electrode active material of the present application, the type and content of the reactants, pH value, type and concentration of precipitating agent, type and concentration of complexing agent, reaction temperature, stirring rate, reaction time, sintering temperature and time were determined. It is possible to comprehensively adjust and control the positive electrode active material so that the positive electrode active material has the specific chemical composition and structure described in this application, which can greatly improve the electrochemical performance of the positive electrode active material, and finally improve the specific capacity, rate performance and cycle performance of the sodium-ion battery.

Positive pole piece

A second aspect of the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. For example, the positive electrode current collector includes two opposite surfaces, and the positive electrode active material layer is laminated on either or both of the two surfaces of the positive electrode current collector.

The positive electrode current collector can be made of metal foil, carbon-coated metal foil or porous metal plate, preferably aluminum foil.

The positive electrode active material layer includes the positive electrode active material of the first aspect of the present application. Optionally, the positive active material in the positive active material layer is Na _2.2 Cu _1.1 Mn _2.0 O ₇ , Na _2.0 Cu _0.9 Mn _2.0 O ₇ , Na _2.0 Cu _0.6 Mn _2.4 O ₇ , Na _2.0 Cu _0.4 Mn _2.4 Fe _0.2 O ₇ and one or more of Na _2.0 Cu _0.4 Mn _2.4 Zn _0.2 O ₇ .

The positive electrode active material layer also includes a binder and a conductive agent.

The above-mentioned binder can be styrene butadiene rubber (SBR), water-based acrylic resin (water-based acrylic resin), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene - one or more of vinyl acetate copolymer (EVA) and polyvinyl alcohol (PVA).

The above-mentioned conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

The above-mentioned positive electrode sheet can be prepared according to conventional methods in the art. Usually, the positive electrode active material and optional conductive agent and binder are dispersed in a solvent (such as N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector , after drying, cold pressing and other processes, the positive pole piece is obtained.

Since the positive electrode active material of the first aspect of the present application is used, the positive electrode sheet of the present application has high comprehensive electrochemical performance.

sodium ion battery

A third aspect of the present application provides a sodium-ion battery, including the positive electrode sheet of the second aspect of the present application.

The sodium-ion battery also includes a negative pole piece, a separator, and an electrolyte.

The above-mentioned negative pole piece may be a metal sodium piece.

The negative electrode sheet may also include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. For example, the negative electrode current collector includes two opposite surfaces, and the negative electrode active material layer is laminated on either or both of the two surfaces of the negative electrode current collector.

The negative electrode current collector can be made of metal foil, carbon-coated metal foil, or porous metal plate, and copper foil is preferred.

The negative active material layer usually includes negative active materials and optional conductive agents, binders and thickeners. The negative active materials can be natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon and soft carbon medium. one or more, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, and the binder can be It is one or more of styrene-butadiene rubber (SBR), water-based acrylic resin and carboxymethyl cellulose (CMC). The thickener can be carboxymethyl cellulose (CMC). However, the present application is not limited to these materials, and other materials that can be used as negative electrode active materials, conductive agents, binders, and thickeners for sodium ion batteries can also be used in the present application.

The above-mentioned negative pole pieces can be prepared according to conventional methods in the art. Usually, the negative electrode active material and optional conductive agent, binder and thickener are dispersed in a solvent, which can be deionized water, to form a uniform negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector, After drying, cold pressing and other processes, the negative pole piece is obtained.

The above-mentioned separator is not particularly limited, and any well-known porous structure separator with electrochemical stability and chemical stability can be selected, such as glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. One or more of the single-layer or multi-layer films.

The above-mentioned electrolytic solution may include an organic solvent and an electrolyte sodium salt. As an example, the organic solvent may be one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC); the electrolyte sodium salt may be NaPF _6. One or more of NaClO ₄ , NaBCl ₄ , NaSO ₃ CF ₃ and Na(CH ₃ )C ₆ H ₄ SO ₃ .

The above-mentioned positive pole piece, separator, and negative pole piece are stacked in sequence, so that the separator is placed between the positive pole piece and the negative pole piece to play a role of isolation to obtain a battery core, or a battery core can be obtained by winding ; Place the battery cell in the packaging shell, inject the electrolyte and seal to obtain a sodium ion battery.

Due to the use of the positive electrode active material of the first aspect of the present application, the sodium-ion battery of the present application has high comprehensive electrochemical performance, high first-round discharge specific capacity and energy density, and high rate capability. and cycle performance. Using the positive electrode active material of the present application also increases the electrochemical window of the sodium ion battery, and enables the sodium ion battery to be charged and discharged within a wider electrochemical window without affecting the specific capacity and energy density of the battery .

Example

The following examples describe the disclosure of the present application in more detail, and these examples are provided for illustrative purposes only, as various modifications and changes within the scope of the disclosure of the present application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples are either commercially available or synthesized according to conventional methods, and can be directly Used without further processing, and the instruments used in the examples are commercially available.

Example 1

Preparation of Cathode Active Materials

S10, according to a stoichiometric ratio, copper sulfate pentahydrate and manganese sulfate monohydrate are dissolved in deionized water under the protection of an inert atmosphere to prepare a mixed solution, wherein the total concentration of metal ions is 1.2 mol/L.

S21. Disperse the precipitant sodium carbonate in deionized water to prepare a precipitant solution, wherein the concentration of the sodium carbonate is 4 mol/L. Ammonia with a concentration of 2 mol/L was used as the complexing agent solution.

S22, adding the precipitant solution and the complexing agent solution to the mixed solution to obtain a reaction solution, and controlling the pH value of the reaction solution to be 11.0.

S30. The reaction solution is reacted at 50° C. and a stirring speed of 800 rpm for 20 hours, the obtained co-precipitated product is separated and collected, washed with an appropriate amount of deionized water for several times, and dried in a vacuum drying oven at 100° C. to obtain Transition metal source [Cu _1.1 Mn _2.0 ][CO ₃ ] _3.1 .

S40. Mix the sodium hydroxide and the transition metal source uniformly according to the stoichiometric ratio, and perform sintering treatment at 800° C. in an air atmosphere for 16 hours. After the obtained sintered product is cooled to room temperature, wash the precipitated product with an appropriate amount of deionized water for several times. , and after drying, the positive electrode active material is obtained.

Preparation of button battery

1) Preparation of positive electrode sheet

The above-prepared positive electrode active material, conductive carbon black Super P, and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5 to make the mixture. It forms a uniform positive electrode slurry; the positive electrode slurry is coated on the aluminum foil of the positive electrode current collector, and after drying, it is punched into a circle with a diameter of 14 mm.

2) Preparation of negative pole piece

The sodium metal sheet was punched into a 14mm diameter disc.

3) The separator is made of glass fiber film.

4) Preparation of electrolyte

Equal volumes of ethylene carbonate (EC) and propylene carbonate (PC) are mixed uniformly to obtain an organic solvent, and then sodium perchlorate NaClO is uniformly dissolved in the above _- mentioned organic solvent to obtain an electrolyte, wherein the sodium perchlorate The concentration is 1mol/L.

5) Stack the above-mentioned positive pole piece, separator, and negative pole piece in order, add the above-mentioned electrolyte and seal to obtain a button battery.

Examples 2 to 19 and Comparative Examples 1 to 3

Similar to Example 1, the difference is that the reaction parameters in the preparation step of the positive electrode active material are adjusted. The specific parameters are shown in Table 1 below.

test section

(1) Rate performance test

At 25°C and normal pressure (0.1MPa), the sodium ion batteries prepared in the examples and comparative examples were charged to 4.3V with a constant current rate of 2C, and then discharged to 2.1V with a constant current rate of 2C. Battery 2C rate discharge specific capacity. Four samples were tested for each example and comparative example, and the test results were averaged.

(2) Capacity development and cycle performance test

At 25°C and normal pressure (0.1MPa), the sodium-ion batteries prepared in the examples and comparative examples were charged at a constant current rate of 0.1C to a voltage of 4.3V, and the charging capacity at this time was recorded as the first cycle of the sodium-ion battery. Charge capacity, then stand for 5 minutes, then discharge at a constant current rate of 0.1C until the voltage is 2.1V, and let stand for 5 minutes. This is a cyclic charge-discharge process. The discharge capacity is recorded as the first cycle discharge specific capacity of the sodium-ion battery. That is, the initial capacity of the sodium-ion battery. The sodium-ion battery was subjected to a 300-cycle charge-discharge test according to the above method, and the discharge specific capacity of the 300th cycle was detected.

The capacity retention rate (%) of the sodium-ion battery after 300 cycles = the discharge specific capacity of the 300th cycle/the first cycle discharge specific capacity×100%.

The test results of Examples 1 to 19 and Comparative Examples 1 to 3 are shown in Table 2 below.

Table 1

Table 2

Comparative analysis of Examples 1 to 19 and Comparative Examples 1 to 2 shows that by making the positive active material of the molecular formula Na _2+x Cu _h Mn _k M _l O _7-y satisfies 2≤h+k+l≤3.5 and 0.57≤ (2+x)/(h+k+l)≤0.9, which can significantly improve the comprehensive electrochemical performance of the material, so that the positive electrode active material has a higher capacity, and has both higher rate performance and cycle performance.

In Comparative Example 3, the sodium content of the positive electrode active material is high, the stability of the material to air, water and carbon dioxide is poor, the first cycle discharge specific capacity of the positive electrode active material is low, and the rate performance is poor. The capacity retention rate is low.

To sum up, by making the positive electrode active material have the specific chemical composition mentioned above, the present application significantly improves the first cycle discharge specific capacity, the electrical performance under high current and the capacity retention during the cyclic charge and discharge process of the positive electrode active material. Therefore, the positive electrode active material can take into account high capacity performance, high rate performance and cycle performance at the same time.

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalents within the technical scope disclosed in the present application. Modifications or substitutions shall be covered by the protection scope of this application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (11)

1. A positive electrode active material, characterized in that the molecular formula of the positive electrode active material is Na_2+xCu_hMn_kM_lO_7-yIn the molecular formula, M is a transition metal site doping element, M is L i, B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, Sn, Ba and W, x is more than or equal to 0 and less than or equal to 0.5, and x is more than or equal to 0.1 and less than or equal to 0.5<h≤2，1≤k≤3，0≤l≤0.5，0≤y≤1；

Wherein, h + k + l is more than or equal to 2 and less than or equal to 3.5, and (2+ x)/(h + k + l) is more than or equal to 0.57 and less than or equal to 0.9.

2. The positive electrode active material according to claim 1, wherein in the formula, 0.6. ltoreq. (2+ x)/(h + k + l) is 0.8 or less.

3. The positive electrode active material according to claim 1, wherein in the molecular formula, 0.5. ltoreq. h.ltoreq.1.5, 1.5. ltoreq. k.ltoreq.2.5; preferably, 0.9. ltoreq. h.ltoreq.1.5; more preferably, 0.9. ltoreq. h.ltoreq.1.2.

4. The positive electrode active material according to claim 1, wherein k/(h + l) ≥ 1.4, preferably 1.6 ≤ k/(h + l) ≤ 6.

5. The positive electrode active material according to any one of claims 1 to 4, wherein the specific surface area of the positive electrode active material is 0.01m²/g～20m²A/g, preferably of 0.1m²/g～15m²/g；

And/or the average particle diameter D of the positive electrode active material_v50 is 0.5 to 25 μm, preferably 1 to 15 μm.

6. The positive electrode active material according to claim 1, wherein the positive electrode active material has a triclinic-phase crystal structure or a hexagonal-phase crystal structure;

preferably, the positive electrode active material includes a first diffraction peak at a diffraction angle 2 θ of 15.8 ° to 16.0 ° and a second diffraction peak at a diffraction angle 2 θ of 32.0 ° to 32.2 ° under X-ray diffraction, and the intensity ratio of the first diffraction peak to the second diffraction peak is 5 to 30, the half-width of the first diffraction peak is 0.02 to 0.5 °, and the half-width of the second diffraction peak is 0.02 to 0.5 °.

7. The positive electrode active material according to claim 1, wherein the positive electrode active material has a powder resistivity of 10 Ω · cm to 300k Ω · cm, preferably 20 Ω · cm to 3k Ω · cm, under a pressure of 12 MPa.

8. The positive electrode active material according to claim 1, wherein the positive electrode active material isThe tap density of the material is 0.5g/cm³～3.5g/cm³Preferably 1.5g/cm³～3.0g/cm³；

And/or the positive electrode active material has a compacted density of 2.5g/cm at a pressure of 8 tons³～4.5g/cm³Preferably 3.5g/cm³～4.5g/cm³。

9. The positive electrode active material according to claim 1, wherein the positive electrode active material has a first discharge voltage plateau at 3.8V to 4.1V and a second discharge voltage plateau at 3.4V to 3.7V;

the positive electrode active material has a discharge capacity of Q at the first discharge voltage plateau₁The discharge capacity of the positive active material at the second discharge voltage plateau is Q₂The positive electrode active material has a full discharge capacity of Q, and Q₁、Q₂And Q satisfies:

30％≤(Q₁+Q₂) 100% ≦ 90%, preferably 50% ≦ Q × 100₁+Q₂)/Q×100％≤80％。

10. A positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 9.

11. A sodium ion battery comprising the positive electrode sheet of claim 10.

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